Subject: Re: [PATCH] netfilter: nf_conntrack: use get_unaligned_be32() in tcp_sack()

From: Pablo Neira Ayuso <[email-masked]>
Date: Sun, 7 Jun 2026 11:12:33 +0200

On Sun, Jun 07, 2026 at 11:09:43AM +0200, Pablo Neira Ayuso wrote:
> On Mon, May 25, 2026 at 02:58:40PM -0700, Rosen Penev wrote:
> > The timestamp-only fast path dereferences the option stream as
> > *(__be32 *)ptr, which assumes 4-byte alignment that the TCP option
> > stream does not guarantee. Use get_unaligned_be32() instead, which
> > reads the value safely and already returns host byte order, so the
> > htonl() on the comparison constant can be dropped.
> > 
> > This matches the existing get_unaligned_be32() use later in the same
> > function.
> > 
> > Assisted-by: Claude:Opus-4.7
> > Signed-off-by: Rosen Penev <[email-masked]>
> > ---
> >  net/netfilter/nf_conntrack_proto_tcp.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/net/netfilter/nf_conntrack_proto_tcp.c b/net/netfilter/nf_conntrack_proto_tcp.c
> > index b67426c2189b..8993374c9df2 100644
> > --- a/net/netfilter/nf_conntrack_proto_tcp.c
> > +++ b/net/netfilter/nf_conntrack_proto_tcp.c
> > @@ -405,11 +405,11 @@ static void tcp_sack(const struct sk_buff *skb, unsigned int dataoff,
> >  		return;
> >  
> >  	/* Fast path for timestamp-only option */
> > -	if (length == TCPOLEN_TSTAMP_ALIGNED
> > -	    && *(__be32 *)ptr == htonl((TCPOPT_NOP << 24)
> > -				       | (TCPOPT_NOP << 16)
> > -				       | (TCPOPT_TIMESTAMP << 8)
> > -				       | TCPOLEN_TIMESTAMP))
> > +	if (length == TCPOLEN_TSTAMP_ALIGNED &&
> > +	    get_unaligned_be32(ptr) == ((TCPOPT_NOP << 24) |
> > +					(TCPOPT_NOP << 16) |
> > +					(TCPOPT_TIMESTAMP << 8) |
> > +					TCPOLEN_TIMESTAMP))
> 
> Missing put_unaligned_be32(), BTW.

Sorry, no write in this case, only read, LGTM. Apologies.

> >  		return;
> >  	while (length > 0) {
> > -- 
> > 2.54.0